She also urged it not to recognize Jerusalem as Israel's capital - a campaign promise of US president Donald Trump, euobserver.com reported.

"The Iran nuclear deal is a key strategic priority for European security, but also for regional and global security," Mogherini said.

"Dismantling an agreement on nuclear issues that is working - as the International Atomic Energy Agency has certified nine times - would not put us in a better position to discuss all the rest on the country," she added.

Mogherini said "a way must be found, through negotiations, to resolve the status of Jerusalem’ as the future capital of both sides, referring to Israel and Palestine's conflict over the city.

"We believe that any action that would undermine this effort must absolutely be avoided," she said.

She spoke at a short press conference in which reporters were not allowed to ask questions.

Her remarks came after Trump, two months ago, asked Congress to unilaterally scrap the Iran accord. The deal, which involves lifting sanctions in return for curbing Iran’s nuclear activities, was negotiated by Mogherini in its final stages.

The EU chief diplomat's comments also came amid White House signals that Trump will say, this week, that the US would move its Israel embassy from Tel Aviv to Jerusalem, in a de facto recognition of Israel's claim to the city.

Tillerson on Iran

Tillerson at first appeared to contradict Trump on scrapping the Iran deal.

"We discussed … our joint efforts under the Joint Comprehensive Plan of Action [the Iran accord] to hold Iran fully compliant with the terms of that deal and fully enforce that agreement", he said after meeting Mogherini.

He then echoed Trump, saying Iran should pay a price for its activities in the Middle East.

He cited Iran's ballistic missile program, its support for Yemen, for the Syrian government, and for Hezbollah, an armed militia in Lebanon, among the issues.

"These … activities of Iran cannot be ignored and cannot go unanswered and we intend to continue to take action to ensure Iran understands this," he said.

Iran has repeatedly said its missile program is defensive and rejected the possibility of any negotiation on it.

He said nothing on Jerusalem.

But he listed other areas in which the EU and US were in agreement: on countering Russia's aggression in Ukraine, sanctions on North Korea's nuclear program, fighting terrorism, and spending more on NATO defense.

"The partnership between America and the European Union ... is based upon shared values, shared objectives for security and prosperity on both sides of the Atlantic and we remain committed to that," Tillerson said.

Tillerson's meeting with Mogherini was the first in a series of events in Brussels on Tuesday and Wednesday.